Lithium primary batteries include a positive electrode including a positive electrode active material such as manganese dioxide or fluorinated graphite, a negative electrode comprising lithium or a lithium alloy, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte being in contact with the positive electrode, the negative electrode, and the separator. Lithium primary batteries have a high electromotive force and a high energy density and therefore are widely used as a main power source for portable equipment, vehicle-mounted electronic equipment, and the like, a backup power source, and other applications.
Generally, lithium primary batteries exhibit a drop in voltage at the beginning of discharge, followed by a slow increase in voltage. The larger the degree of the drop in voltage at the beginning of discharge is, the lower the discharge performance of lithium primary batteries is. In this context, attempts have been made to activate the surface of the negative electrode in order to improve the discharge performance. In a lithium primary battery including a negative electrode having an activated surface, however, the battery characteristics after storage at high temperature are significantly deteriorated. This is because the reaction between the activated negative electrode and the non-aqueous electrolyte is facilitated due to the high temperature, and a reaction product is deposited on the surface of the negative electrode, causing the resistance at the surface of the negative electrode to increase.
On the other hand, in the case of lithium secondary batteries, which include a negative electrode containing lithium or a lithium alloy, lithium in the negative electrode is repeatedly dissolved and precipitated during charge/discharge cycling. As such, the surface of the negative electrode of lithium secondary batteries is renewed every charge/discharge cycle and thus is maintained in a low resistance state. In lithium secondary batteries, however, dendritic crystals (dendrites) of lithium may grow on the surface of the negative electrode as the charge/discharge cycle is repeated.
Japanese Laid-Open Patent Publication No. Hei 11-135116 discloses a negative electrode for a lithium secondary battery, the negative electrode comprising metal lithium or a lithium alloy and a carbon powder layer formed on the surface of the metal lithium or lithium alloy. Japanese Laid-Open Patent Publication No. 2002-141058 discloses a negative electrode for a lithium secondary battery, the negative electrode comprising an electrically conductive substrate, a lithium layer containing metal lithium or an alloy thereof and being formed on the surface of the conductive substrate, and a metal fluoride layer being made of lithium fluoride or the like and formed on the surface of the lithium layer.